Austempered, cold-finished steels



United States Patent AUSTEMPERED, COLD-FINISHED STEELS Elliot S. Nachtman, Park Forest, 11]., assignor to LaSalle Steel Co., Hammond, lnd., a corporation of Delaware No Drawing. Application October 22, 1956 Serial No. 617,268

8 Claims. (Cl. 148-12) This invention relates to a new and improved metallurgical process applicable to the cold finishing of steels and it relates to a process of the type described capable of producing steelshaving new and improved characteristics and new and improved combinations of properties.

This invention is related to the processes described in the copending applications Ser. No. 518,411, Ser. No. 518,412, Ser. No. 518,413 and Ser. No. 518,414, filed June 27, 1955 now Patents No. 2,767,837, No. 2,767,- 835, No. 2,767,836, and No. 2,767,838, respectively.

It is an object of this invention to produce and to provide a method for producing new and improved steels having new and different physical and mechanical properties and combinations thereof.

More specifically, it is an object of this invention to provide a method, adapted foruse in the cold finishing of steels, which may be employed to improve certain physical and mechanical properties in the steel, which may be employed to produce steels having new and different combinations of properties thereby to provide new and improved steel products which provide for greater uniformity in properties and characteristics of the steels of corresponding chemistry from heat to heat by comparison with the normal hot rolled steels which are cold finished, which may be employed to expand the range of physical and mechanical properties capable of being developed in the steels thereby to open up new and difierent areas of use, and it is a related object to produce steels having new and improved characteristics and new and improved physical and mechanical properties.

In the aforementioned copending applications, description is made of a metallurgical process which may be employed in the cold finishing of steel to improve physical and mechanical properties of the steel. The metallurgical process defined is based upon an elevated temperature reduction step wherein, for example, the steel is advanced through a die to take a reduction in crosssectional area while the steel is at a temperature within the range of 200 F. to the lower critical temperature for the steel composition or while the steelis at a temperature within the range of 200 F. to 1100-1200 F. Dependin upon the temperature of the steel reduced in the elevated temperature reduction step, various physical and mechanical properties of the steel can be changed, and in many instances materially improved, by comparison with the same steels given an equivalent reduction but while the steel is at room temperature. Thus, by controlling the temperature of the steel in the elevated temperature reduction step, by controlling the chemistry of the steel and by controlling the amount of reduction, it has become possible to produce new and improved steel products having new and improved physical and mechanical properties and dilierent combinations thereof.

In my copending application filed concurrently herewith and entitled Cold Finished Steels and Method for the Manufacture of Same, Ser. No. 617,264, description is made of a modification in the elevated temperature reduction concept wherein, prior to the elevated tem- 2,881,107 Patented Apr. 7,195 9 2 perature reduction step, the steel is heated to austenitizing temperature followed by quenching to produce a phase change in the steel wherein the steel is characterized by the presence of bainite and martensite, alone or in combination. In another copending application filed concurrently herewith and entitled Metallurgical Process for Cold Finishing Steel, Ser. No. 617,266, description is made of another modification which embodies the elevated temperature reduction concept wherein the steel, prior to taking the elevated temperature reduction step, is austenitized by heating above its transformation range and quenched to effect the described phase change followed by tempering the quenched steel. In each of these processes, utilization continues to be made of the characeristics in the steel whereby improvements are secured in physical and .mechanical properties by reduction in cross-section when worked at elevated temperatures.

The process forming the subject matter of this invention embodies a still further modification in the elevated temperature reduction concept. In accordance with the practice of this invention, the hot rolled steels are processed through a combination of steps which includes the step of austempering the hot rolled steel and then advancing the steel through a die to effect the desired reduction in cross-sectional area while the steel is at a temperature within the range of 200 F. to the lower critical temperature for the steel composition and preferably while the steel is at a temperature within the range of 450 F. to the lower critical temperature for the steel composition. The combination of steps which includes austempering the steel prior to taking the elevated temperature reduction step results in the formation of steels characterized by improvements in the strength properties of the steels and in the hardness of the steels over similar steels given an equivalent reduction at elevated temperature without previous austempering and over steels given an equivalent reduction in cross-sectional area by cold drawing following austempering.

Included amongst the physical and mechanical properties which are influenced by the concepts described are the strength properties of the steel, such as tensile strength, impact strength, yield strength, fiexural strength and the like and such other properties as elasticity, elongation, hardness, surface roughness, machinability, proportional limits and the like. The most significant improvements developed in steels processed in the manner described are the strength properties of the steel and its hardness.

The characteristics described are capable of development with hot rolled steels of the type which are generally cold finished, as by the processes of drawing or extrusien. Steels which exhibit improvements when processed in accordance with the practice of this invention are similar to those which are beneficially afiected by the elevated temperature reduction steps described in the aforementioned copending applications. Such steels are characterized by the ability to strain harden or harden by some mode of precipitation or other re-arrangement when worked at an elevated temperature within the range of 200 F. to the lower critical temperature for the steel composition. Representative are the non-austenitic steels having a pearlitic structure in a matrix of free ferrite. While steels containing carbon over a fairly wide range can be employed, as defined in the aforementioned copending applications, best results are secured in the practice of this invention in the processing of steels having a carbon content greater than 0.040 percent.

' In the process embodying the features of this invention, the temperature of the steel in the elevated temperature reduction step, the chemistry of the steel and the amount of reduction influence the level of improvements which 5 are secured and the combination of characteristics and properties .tbat are capable of being developed. in the-:steel "characteristics and properties developed in the steel other than the fact that rapid cooling tends to produce steels having a preponderance of compressive stressesto provide steels characterized by negative warpage values, especially when :the elevated temperature reduction step is taken .whilethesteel 'is-at-a temperature of above 700 F.

As .used herein, the term elevated temperature reduction (ETD) :is meant to include the step of processing the :steel wherein the steel is advanced through a die,

such asa draw die, extrusion *die 'or roller die, 'toeffect reductionin cross-sectional area 'while the steel is at a temperaturewithin the-range of 200 F. to the lower critical temperature for the steel compositionand preferably'while the steel is at'a temperature within the range of 450 F. to -1 100-1200 F. While not equivalent from the standpoint of the process, many of the-characteristics described-are capable of being-developed by other methods for working the steel to effect reduction in'crosssectional area while the steel is at the desired elevated temperature. For example, many of the described "improvements are secured in steels which have been austempered and then reduced in cross-section by rolling while the steel is at a temperature within the range of 200 F. to the lower critical temperature for the steel composition.

The term"austempering is intended to have the same meaning as is normally applied to the term in the art. Briefly described, austempering -'is intended torelate to -a special heat treating process wherein the steel heated to a temperature above the transformation range or to a temperature within the range of 1500-l600 F. is

quenched in a medium having a rate of heat abstraction sufficiently high to prevent the formation of high temperature transformation products and maintaining the steel at a temperature below that of pearlitic formation and above that of martensite formation (M until transformation is complete.

The following will illustrate the practice of this invention with 4140 steel, which maybe considered as representative of the steels capable of being improved The hot rolled steel bars, as received, weredescaled by pickling in sulphuric acid and limed to prevent rusting. The pickled and limed bar stock was then heated in a suitable heat treating furnace to a temperature of 1550 F. for about 45 minutes. The austenitized steel was then quenched in a salt bathmaintained at a temperature of 640 P. which is slightly above the martensite formation range and which causes heat abstraction at a rate to avoid'passage of the steel through .the pearlitic range. The steel was held .in the bath for a time sufficient to reduce the temperature uniformly through the steel to about 640 F. (about 16 minutes), and-thenthe steel was cooled to room temperature as'by-means of a quench or by air cooling.

It will be understood that the process of austempering to produce a steel having a low temperature transformation structure is well known to those skilled in the art such that detaileddesctiption of .the various modifications with respect tothe time and temperature relationshipneed not beset forth in greaterdetail.

The austempered steelwas reheated -to adesired temperature for advancement through the 'die to effect reduction in cross-sectional area. Asuitable drawing compound was applied to the surfaces of the austempered steel and the steel was advanced through a draw die to effect reduction in cross-sectional area.

The properties developed in the steel will hereinafter 'be:set forth in the-following table. The advantage of quenching, as compared to air cooling, after drawing appears to reside principally in the'reduction of residual stress characteristics, especially when use is made of a temperature in the upper range-preferably above 700 'F., in the elevated temperature reduction step. As a result, it will be expedient, in the data hereinafter presented, merely to set forth the values secured 'as a result of air cooling following drawing. ,It-willbe understood that similar properties, other than lower residual stress characteristics, will be 'secured by quenching the steel in oil or waterafterthe elevated temperature reduction step.

"In the data hereinafter -set forth, comparisons will also be made with the value secured with the samesteel, as received in hot rolled condition,'with 'the same steel cold drawn -to effect equivalent reduction in cross-sectional area, with the same steel drawn at elevated temperature'without previous heat treatment to austemper the steel, with the same steel as quenched to room temperature and austempered by quenching from 640 F. In the drawing operations, 41'40steel of inch round 'by the concepts described and which has the "following was drawn to take areduction of 19.9' percent.

Table I ;[4140;steel:austempered at;1550;F. and quenched to 640?F. Drawn to take a'ltm-pcreent' reduction-air cooled after. drawing] .Tenslle I ,Yleld .Elongm. Reduot Hardness DBH -.Temp.'*oi. Draw,'jF. Pull, fStrength, fStrength," tion, .area,

Lbs .;,p.s.1. p.51. 1 jPercent Percent S MR 0 )I t B011 140,000 105, 750. 15. 02 x42. 8 .310 an 301 Cold Drawn..- 18,'-320 1 {000 '153, 9.0' 48.9 324 330 324 RT 15, 171- 195, 000 191, 250 10. 0 36; 7 389 402 402 'As quenched (O) 292,000 246, 000 12.9 44.1 .600 429 468 Austemper Quench From 640 F. 178, 000 136, 250 13.6 57. 4 378 307 307 690 27,480 217, 000 217, 000 9. a v 45. 7 425 462 479 20, 610 184, 000, .180, 260 15. 0 52. 6 391 333 328 220 141, 000 120, 000 21. 4 58. 5 310 307 302 1 Data at approximate peak of ETD curve. 4 conventionally quenched in 011 to room temperature.

ladle"analysis'in'which the majoringredients other than iron are set forth:

Fromtthe results-given, it -will.be-;apparent that im- -Cafbo 3 'provements are-secured in zthestrength properties ofthe Manganese 38 steel and in-hardness whenthesteelsare processed in Phosphorus .018 accordance with the practiceofjthis invention by com- SulPhur .020 .parison with elevated temperature reduction alone and Silicon- .26 overcold drawn steels, with or without previously aus- Chromium. .86 tempering.

Molybdenum .18 It will be evident that by the combination of steps BAA comprising austempering and elevated temperature reduction improvement can be introduced into steel products thereby to provide a new and improved steel having improved characteristics and different combinations of characteristics by comparison with steels of the type heretofore capable of being produced by various processing techniques.

It will be understood that the invention may be practiced on steel rods, Wires, tubing and the like, as well as on bar stock and that changes may be made with respect to the techniques of heating and cooling the steel and in their method of handling through the various process steps without departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. The metallurgical process of treating steel of the non-austenitic type having a pearlitic structure in a matrix of free ferrite comprising the combination of steps of austempering the steel and then advancing the austempered steel through a die to effect a reduction in crosssectional area while the steel is at a temperature within the range of 200 F. to the lower critical temperature for the steel composition.

2. The metallurgical process of treating steel which strain hardens and which hardens by some mode of precipitation when worked at a temperature within the range of 200 F. to the lower critical temperature for the steel composition comprising the combination of steps of austempering the steel and advancing the steel through a die to efiect a reduction in cross-sectional area by a drawing operation while the steel is at a temperature within the range of 200 F. to the lower critical temperature for the steel composition.

3. The metallurgical process of treating steel which strain hardens and which hardens by some mode of precipitation when worked at a temperature within the range of 200 F. to the lower critical temperature for the steel composition comprising the combination of steps of austempering the steel and advancing the steel through an extrusion die to effect a reduction in crosssectional area by an extrusion operation while the steel is at a temperature within the range of 200 F. to the lower critical temperature for the steel composition.

4. The metallurgical process of treating steel which strain hardens and which hardens by some mode of precipitation when worked at a temperature within the range of 200 F. to the lower critical temperature for the steel composition comprising the combination of steps of austempering the steel and rolling the steel to effect a reduction in cross-sectional area by a rolling operation while the steel is at a temperature within the range of 200 F. to the lower critical temperature for the steel composition.

5. The metallurgical process of treating steel which strain hardens and which hardens by some mode of precipitation when worked at a temperature within the range of 200 F. to the lower critical temperature for the steel composition comprising the combination of steps of austempering the steel and advancing the steel through a die to efiect a reduction in cross-sectional area while the steel is at a temperature Within the range of 200 F. to the lower critical temperature for the steel composition, and air cooling the steel after the elevated temperature reduction step.

6. The metallurgical process of treating steel which strain hardens and which hardens by some mode of precipitation when worked at a temperature within the range of 200 F. to the lower critical temperature for the steel composition comprising the combination of steps of austempering the steel and advancing the steel through a die to effect a reduction in cross-sectional area while the steel is at a temperature Within the range of 200 F. to the lower critical temperature for the steel composition, and quencing the steel rapidly to cool the steel after the elevated temperature reduction step.

7. The metallurgical process of treating steel which strain hardens and which hardens by some mode of precipitation when worked at a temperature within the range of 450 F. to the lower critical temperature for the steel composition comprising the combination of steps of austempering the steel and advancing the steel through a die to etfect a reduction in cross-sectional area while the steel is at a temperature within the range of 450 F. to the lower critical temperature for the steel composition.

8. A steel having new and improved physical and mechanical properties produced by the method of claim 5 Metals Handbook, 1948 ed., pages 286 and 629.

Pomp: The Manufacture and Properties of Steel Wire, copyright 1941, English translation, 1954, pages 205-233 and 92-93. 

1. IN THE PRODUCTION OF DRY SOYBEAN MATERIAL THE STEPS
 1. THE METALLURGICAL PROCESS OF TREATING STEEL OF THE NON-AUSTENITIC TYPE HAVING A PEARLITIC STRUCTURE IN A MATRIX COMPRISING SUBJECTING SOYBEAN MATERIAL CONTAINING NATURAL WATER-SOLUBLE INGREDIENTS TO THE DISSOLVING ACTION OF WATER OF FREE FERRITE COMPRISING THE COMBINATION OF STEPS OF AUSTEMPERING THE STEEL AND THEN ADVANCING THE AUSTEMAT A PH IN THE VICINITY OF THE ISOELECTRIC PH OF THE GLYCININ CONTENT OF SAID MATERIAL, SEPARATING SOLIDS FROM THE RESULTPERED STEEL THROUGH A DIE TO EFFECT A REDUCTION IN CROSSSECTIONAL AREA WHILE THE STEEL IS AT A TEMPERATURE WITHIN ING SOLUTION, REMOVING SUBSTANTIALLY ALL OF THE BEANY-TASTE INGREDIENTS FROM RESULTING SOLIDS BY WASHING WITH WATER, THE RANGE OF 200* F. TO THE LOWER CRITICAL TEMPERATURE FOR THE STEEL COMPOSITION. AND DRYING THE SOLIDS CONTENT WHEREBY TO PROVIDE A HIGHYIELD SOY PRODUCT. 